Ask Slashdot: How can Free Web Service Recoup Costs?

Trixter asks this question, which might be helpful to any of you out there that might be looking to do something similar: "I'm planning a huge, free, online resource, and am just looking for a way to recoup any operating costs; I'm providing the server out of my own pocket, but would like advertising to pay for the bandwidth each month, with any additional profits going into upgrading the server hardware and bandwidth, ad infinitum. Just how do you make money on the web with a free service?"